GraphTED - graphene nanocomposite materials for thermoelectric devices

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The Seebeck effect is a thermoelectric effect whereby a temperature gradient across a material is converted to a voltage,which can be exploited for power generation. The growing concern over fossil fuels and carbon emissions has led todetailed reviews of all aspects of energy generation and routes to reduce consumption. Thermoelectric (TE) technology,utilising the direct conversion of waste heat into electric power, has emerged as a serious contender, particular forautomotive and engine related applications. Thermoelectric power modules employ multiple pairs of n-type and p-type TEmaterials. Traditional metallic TE materials (such as Bi2Te3 and PbTe), available for 50 years, are not well suited to hightemperature applications since they are prone to vaporization, surface oxidation, and decomposition. In addition many aretoxic. Si-Ge alloys are also well established, with good TE performance at temperatures up to 1200K but the cost per wattcan be up to 10x that of conventional materials. In the last decade oxide thermoelectrics have emerged as promising TEcandidates, particularly perovskites (n-type) and layered cobaltites (e.g. p-type Ca3Co4O9) because of their flexiblestructure, high temperature stability and encouraging ZT values, but they are not yet commercially viable. Thus thisinvestigation is concerned with improving the thermoelectric properties of oxide thermoelectrics, specifically StrontiumTitanate (n-type) and Bismuth Strontium Cobaltite (p-type).The conversion efficiency of thermoelectric materials is characterised by the figure of merit ZT (where T is temperature); ZTshould be as high as possible. To maximise the Z value requires a high Seebeck coefficient (S), coupled with small thermalconductivity and high electrical conductivity. In principle electrical conductivity can be adjusted by changes in cation/anioncomposition. The greater challenge is to concurrently reduce thermal conductivity. However in oxide ceramics the latticeconductivity dominates thermal transport since phonons are the main carriers of heat. This affords the basis for a range ofstrategies for reducing heat conduction; essentially microstructural engineering to increase phonon scattering. Byintroducing small pieces of graphene into the oxide it is possible to produce composites which have reduced thermalconductivity and increased electrical conductivity. In this way the ZT characteristics of both Strontium Titanate (n-type) andBismuth Strontium Cobaltite (p-type) can be enhanced. We will prepare composites of the two oxides, determine theirstructures, their phase content and thermoelectric properties. After validation we will construct thermoelectric modulesusing the p-type and n-type composites which will be evaluated in commercially-relevant test environments.